In silver halide color photography, exposed silver halide grains are reduced with an aromatic primary amine color developing agent, and the resulting oxidized product of the developing agent enters into coupling with couplers which form yellow, magenta and cyan dyes.
Pyrazolone couplers are commonly used as the magenta dye forming coupler, but they have various problems. First, they have an undesired absorption in the wavelength range of 400-500 nm in addition to the desired predominant absorption by the magenta dye in the region of 540-560 nm. Secondly, the couplers have low maximum color density and sensitivity. Thirdly, these couplers do not have sufficient long-term stability and a raw photographic material that has been stored in the presence of formalin experiences a change in color shade and a reduction in color formability upon color development.
In order to solve these problems, many proposals have been made in the past. Japanese Patent Application (OPI) No. 42045/1983 (the symbol OPI as used herein means an unexamined published Japanese patent application) shows a coupler having good spectral absorption characteristics with a fairly long absorption wavelength at 552 nm. However, this coupler is not considered to be practical since it has low color sensitivity and density, as well as poor dispersion stability.
Japanese Patent Publication No. 16058/1974 shows a compound having good sensitivity and a fairly long absorption wavelength at 551 nm. However, this compound also has an undesired absorption in the range of 400 to 500 nm, and the color density of the compound is low.
U.S. Pat. No. 3,684,514 shows a compound that is high in both color sensitivity and color density. However, the absorption wavelength of the compound is as short as 543 nm, and the keeping quality of the compound in the presence of formalin is very poor.
Japanese Patent Application (OPI) No. 42045/1983 also shows using said coupler in combination with a certain phenolic compound. However, the absorption wavelength of the combination is still long (558 nm) and no significant improvement is achieved in color sensitivity.
European Pat. No. 74745 shows using a pyrazolone magenta coupler together with the phenolic compound defined in the present invention, but none of the advantages achieved by the present invention are suggested in this patent.
Active efforts have also been made to improve the performance of couplers by mixing with various additives. However, it is impossible to reduce the undesired absorption of pyrazolone magenta couplers by incorporation of other additives. It is therefore desired to improve the pyrazolotriazole magenta couplers shown in Japanese Patent Application (OPI) No. 42045/1983 and British Pat. No. 1,252,418. The advantages of pyrazolotriazole magenta couplers are the absence of any undesired absorption, minimum deterioration of a raw material in the presence of formalin, and high color formability. On the other hand, these couplers are not highly suitable for incorporation in silver halide emulsions because they are so instable in a dispersion that crystal will be easily precipitated. Furthermore, the resulting dye image has a spectral absorption wavelength shorter than the desired value.
When the ballast shown in Japanese Patent Application (OPI) No. 42045/1983 is incorporated in a pyrazolotriazole magenta coupler, the spectral absorption wavelength is shifted to a longer range, but then, high color formability, one great advantage of the pyrazolotriazole magenta coupler, is impaired, and its poor dispersion stability is not at all improved.